(1) Field of the Invention
The present invention relates to a cathode ray tube used in computer monitors, television sets and the like.
(2) Related Art
High-resolution displays are used in computer monitors, CAD systems, CAM systems and digital broadcast receiving devices. Such displays are designed to have more scanning lines than conventional displays used for receiving analog broadcasts. With an increase in the number of the scanning lines, a horizontal deflection frequency of the high-resolution displays also increases. For instance, a conventional display for receiving analog broadcasts (NTSC) has a horizontal deflection frequency of 15.75 kHz, whereas a digital high-definition display has a horizontal deflection frequency of 48 kHz, and some displays for use in computers have a horizontal deflection frequency of as much as 120 kHz.
However, the increased horizontal deflection frequency of the high-resolution display causes problems of a copper-loss in a horizontal deflection coil or an eddy-current loss in core materials, and as a result, raises the temperature of a deflection yoke. This increase in temperature leads to a thermal transformation of an insulating frame supporting deflection coils, causing a change in a deflection magnetic field. This results in degradation in picture quality and a loss of credibility of the high-resolution display. If a display having a higher horizontal deflection frequency is developed in the future, the temperature of the deflection yoke would rise accordingly, and a coating of wires of the deflection coil might peel away.
A technique for preventing the temperature of the deflection yoke from rising is disclosed in Japanese Laid-Open Patent Application No. 05-220343. According to the invention, a coned spacer is mounted between the deflection yoke and a glass bulb, so that the spacer dissipates heat in the deflection yoke to the outside of the deflection yoke.
However, the spacer is made of alumina or the like, and since alumina does not have a high heat transfer property, it fails to produce sufficient heat dissipation effects. On the other hand, when a spacer made of a metal plate or the like is used, due to eddy-currents caused by a deflection magnetic field, the spacer itself comes to produce heat. In that case, it is difficult to efficiently prevent the temperature of the deflection yoke from rising.
Another technique is disclosed in Japanese Laid-Open Patent Application No. 05-21018, in which a compressor or the like provides cooling air in between a deflection yoke and a neck glass to prevent the temperature of the deflection yoke from rising.
However, this construction requires devices such as a compressor and a tube for providing the cooling air to be incorporated in a display device. This not only increases the size of the display device, but also increases power consumption and noise.
The present invention intends to provide a cathode ray tube that is capable of preventing a rise in temperature of a deflection yoke, without increasing the size of a display device.
In order to achieve the above object, the cathode ray tube with a deflection yoke has one or more heat radiators, each of which is made up of filaments, wherein a part of the heat radiator contacts the deflection yoke so that heat is exchanged between the heat radiator and the deflection yoke, while the remaining part of the heat radiator extends outside of the deflection yoke.
In the cathode ray tube, one or more heat radiators are attached so as to contact and exchange heat with the deflection yoke, so that heat in the deflection yoke is conducted through the heat radiators efficiently. In a place where the heat radiator extends outside of the deflection yoke, the heat is dissipated into the air.
Therefore, in the cathode ray tube of the invention, an increase in temperature of the deflection yoke can be efficiently prevented. This is because the filaments made of a metal or other highly conductive materials are not affected by a deflection magnetic field. They do not generate eddy-currents nor produce heat as another heat source.
Furthermore, it is not necessary to incorporate the compressor and the tube for providing cooling air in the cathode ray tube. This does not increase the size of the display device.
It is preferable that the filaments should be made of a paramagnetic or antiferromagnetic metal wire. Specifically, a copper or aluminum wire should be preferably used as a paramagnetic wire, and a chrome wire as an antiferromagnetic wire. Unlike other metal wires with a high heat conductive property, the paramagnetic copper and aluminum wires and antiferromagnetic chrome wires never affect the deflection magnetic field.
It is also preferable to use a cluster strand wire for the filaments. Because a heat radiator made up of the cluster strand wires does not produce any eddy-currents, it can efficiently prevent the temperature of the deflection yoke from rising.
It is also preferable that a heat radiator is formed into a strip by arranging a plural of those metal wires.
It is preferable that each metal wire is individually coated with insulation. Certainly, by using metal wires without insulating coating, contact resistance of the adjacent metal wires can prevent eddy-currents. But metal wires with individual insulation can prevent the occurrence of the eddy-currents with greater efficiency.
For safety reasons, the heat radiators should preferably be electrically insulated at least in a region where it contacts the deflection yoke.
It is preferable that such heat radiators should be placed so as to contact a cone part of the horizontal deflection coil of the deflection yoke, so that heat is exchanged between the heat radiators and the deflection yoke.,This is because the horizontal deflection coil produces a more intense heat than any other part of the deflection yoke does, and because the cone part is heated most.
It is also preferable that the heat radiators should contact the cone part of the deflection yoke in a region along the axis of the cathode ray tube and within 40 mm from a point where the strength of a horizontal deflection magnetic field shows a peak value.
The effect of the present invention can be achieved when each heat radiator is attached to a vertical deflection coil so that heat is exchanged between the heat radiator and the vertical deflection coil.